Some substrates, when placed in a vacuum, display out-gassing during which gaseous matter is emitted from the substrate. This gaseous matter may contaminate the processing equipment and also portions of the substrate itself which is undesirable. Substrates which include organic compounds tend to display out-gassing when placed in a vacuum.
Semiconductor chips are typically provided in a package which includes an organic compound such as a plastic molding compound. The package protects the semiconductor chip which was sawn from a wafer and also provides the link between the semiconductor material's contacts and the external contact areas of the package by which the package is mounted onto a higher level rewiring substrate such as a printed circuit board.
As the complexity of circuits increases, so too does the number of contacts, and this means new types of package are required. The necessary contacts for simple chips can be accommodated just along the edges of the package, but the whole of the base of the package is needed for complex chips. Contacts can take the form of pins or of balls arranged in a matrix pattern. Sometimes a chip is so complex that the package actually has to be larger than is necessary for the chip alone in order to squeeze in all of the contacts.
Some types of packaging, such as that disclosed in U.S. Pat. No. 7,009,288, use a rewiring substrate in the form of prefabricated rewiring board onto which the semiconductor chip is mounted before being electrically connected to the rewiring substrate by bond wires or solder balls, for example. The semiconductor chip and the electrical connections are usually embedded in a plastic composition which forms the housing of the package and protects the semiconductor chip and the electrical connections from the environment.
eWLB (embedded wafer-level ball grid array) technology can match the package to the space required for the balls irrespective of the size of the actual chip, which means packages that are barely any larger than the silicon chip itself. This type of packaging may be provided by first embedding a plurality of semiconductor chips in a plastic housing composition to form a composite wafer and then afterwards depositing a rewiring structure on the composite wafer to provide the electrical connections from the chip contact pads to external contact pads of the package. An example of such a method is disclosed in U.S. Pat. No. 7,202,107.
However, improvements to apparatus and methods for processing a substrate that displays out-gassing, such as a composite wafer, are desirable.